1. Field of the Invention
This invention relates to a radiation image recording and read-out system for exposing a stimulable phosphor to a radiation to have a radiation image stored therein, scanning the stimulable phosphor with a stimulating ray to cause the stimulable phosphor carrying the radiation image to emit light in the pattern of the radiation image stored therein, reading out the emitted light to obtain an electric signal, and reproducing a visible image by use of the obtained electric signal. More particularly, this invention relates to a radiation image recording and read-out system in which the stimulable phosphor is circulated and reused to record radiation images.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to a stimulating ray such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473 and 4,315,318, U.S. patent application Ser. No. 220,780, U.S. Pat. No. 4,387,428, Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use the stimulable phosphor for recording a radiation image of the human body for medical diagnosis. Specifically, the stimulable phosphor is first exposed to a radiation to have a radiation image stored therein, and is then scanned with a stimulating ray which causes it to emit light in the pattern of the stored image. The light emitted from the stimulable phosphor upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image of a quality suitable for viewing and diagnostic purposes. The final visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). The stimulable phosphor sheet used in this method may be in any of various forms such as a panel, drum or the like, which are herein generally referred to as sheets. In this radiation image recording and reproducing method, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
In order to reuse the stimulable phosphor sheet, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with a stimulating ray to read out the radiation image stored thereon should be eliminated or erased by the method described, for example, in Japanese Unexamined Patent Publication No. 56(1981)-11392 or 56(1981)-12599. Practically, it is possible to save manpower by supplying the stimulable phosphor sheet to an image erasing apparatus by use of a conveying means such as a belt conveyor after the radiation image is read out from the stimulable phosphor sheet, and returning the stimulable phosphor sheet to the image recording section by use of a similar conveying means after the radiation image remaining on the stimulable phosphor sheet is erased.
In general, however, it is not easy to design and manufacture a conveying means which can convey a sheet material like the stimulable phosphor sheet without any failure due to clogging, sheets caught at an intermediate point, or the like. Further, the stimulable phosphor sheet must be conveyed in the intact form without being scratched or flawed. This also makes it difficult to design and manufacture the conveying means. Furthermore, it sometimes happens that some phosphor sheets are processed for reproducing the radiation images therefrom immediately after the radiation images are recorded thereon, and some are processed later together with the others. As a result, the sequence of using the phosphor sheets is disordered, and the new and old phosphor sheets are sent in the mixed form to the image recording section. In this case, it is impossible to obtain reproduced images of a uniform quality since the quality of the reproduced images differs between the new and old phosphor sheets. Thus, it is desired to replace the old phosphor sheets with new ones when necessary. For this purpose, it is necessary to inspect the quality of images reproduced from the respective phosphor sheets or to control the number of repetitions of the recording operations for the respective phosphor sheets, thereby to determine whether to replace the phosphor sheets with new ones or to reuse them for further recording operations. However, it is very troublesome to conduct quality control for individual phosphor sheets.
Further, in a movable X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with the radiation image recording and read-out system and travels for recording radiation images for the purpose of collective medical examination, the amount of the recording materials capable of being loaded on the movable radiographic station is limited. Therefore, it is desired to load the stimulable phosphor sheets which can be used repeatedly on the movable radiographic station, once store the radiation images of the objects on the phosphor sheets, transfer the electric image signals read out from the phosphor sheets into a recording medium having a large storage capacity, such as a magnetic tape, circulate and reuse the phosphor sheets for further recording and read-out operations, thereby to obtain the radiation image signals of many objects. In this case, it is not necessary to load a number of stimulable phosphor sheets or panels having a relatively large size (for example, having a size of a conventional X-ray film cassette).
Particularly, when the elements of the system, e.g. the circulatable and reusable recording materials formed of a stimulable phosphor, the image recording section for exposing each recording material to a radiation passing through the object, the image read-out section for reading out the radiation image stored in the recording material, and the erasing means for erasing the radiation energy remaining on the recording material after the read-out step to again record another radiation image thereon, are combined into one unit, the system can easily be loaded on the movable radiographic station for traveling to conduct medical examination and can also be easily installed in a hospital or the like. This is very advantageous in practical use.